Method and apparatus for sidelink identifier change in a wireless communication system

ABSTRACT

A method and apparatus are disclosed from the perspective of a first UE (User Equipment) to update Layer-2 Identities (IDs). In one embodiment, the method includes the first UE establishing a unicast link with a second UE, wherein a first Layer-2 ID of the first UE and a second Layer-2 ID of the second UE are used for data transmission and reception on the unicast link. The method further includes the first UE transmitting a Link Identifier Update Request message for the unicast link to the second UE, wherein the Link Identifier Update Request message includes a new first Layer-2 ID of the first UE. The method also includes the first UE receiving a Link Identifier Update Accept message for the unicast link from the second UE, wherein the Link Identifier Update Accept message includes a new second Layer-2 ID of the second UE. In addition, the method includes the first UE passing the new first Layer-2 ID of the first UE and the new second Layer-2 ID of the second UE down to the lower layer(s) after a Link Identifier Update Acknowledgement (ACK) message is passed to the lower layer(s) for transmission in response to reception of the Link Identifier Update Accept message.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and is a continuation of U.S.Application No. 17/338,860, filed on Jun. 4, 2021, entitled “ METHOD ANDAPPARATUS FOR SIDELINK IDENTIFIER CHANGE IN A WIRELESS COMMUNICATIONSYSTEM”, which claims priority to and is a continuation of U.S.Application No. 17/132,794, filed on Dec. 23, 2020, entitled “ METHODAND APPARATUS FOR SIDELINK IDENTIFIER CHANGE IN A WIRELESS COMMUNICATIONSYSTEM”, which claims the benefit of U.S. Provisional Pat. ApplicationSerial No. 62/991,266 filed on Mar. 18, 2020. The entire disclosure ofU.S. Application No. 17/338,860, the entire disclosure of U.S.Application No. 17/132,794 and the entire disclosure of U.S. ProvisionalPat. Application Serial No. 62/991,266 are incorporated herein in theirentirety by reference.

FIELD

This disclosure generally relates to wireless communication networks,and more particularly, to a method and apparatus for sidelink identifierchange in a wireless communication system.

BACKGROUND

With the rapid rise in demand for communication of large amounts of datato and from mobile communication devices, traditional mobile voicecommunication networks are evolving into networks that communicate withInternet Protocol (IP) data packets. Such IP data packet communicationcan provide users of mobile communication devices with voice over IP,multimedia, multicast and on-demand communication services.

An exemplary network structure is an Evolved Universal Terrestrial RadioAccess Network (E-UTRAN). The E-UTRAN system can provide high datathroughput in order to realize the above-noted voice over IP andmultimedia services. A new radio technology for the next generation(e.g., 5G) is currently being discussed by the 3GPP standardsorganization. Accordingly, changes to the current body of 3GPP standardare currently being submitted and considered to evolve and finalize the3GPP standard.

SUMMARY

A method and apparatus are disclosed from the perspective of a first UE(User Equipment) to update Layer-2 Identities (IDs). In one embodiment,the method includes the first UE establishing a unicast link with asecond UE, wherein a first Layer-2 ID of the first UE and a secondLayer-2 ID of the second UE are used for data transmission and receptionon the unicast link. The method further includes the first UEtransmitting a Link Identifier Update Request message for the unicastlink to the second UE, wherein the Link Identifier Update Requestmessage includes a new first Layer-2 ID of the first UE. The method alsoincludes the first UE receiving a Link Identifier Update Accept messagefor the unicast link from the second UE, wherein the Link IdentifierUpdate Accept message includes a new second Layer-2 ID of the second UE.In addition, the method includes the first UE passing the new firstLayer-2 ID of the first UE and the new second Layer-2 ID of the secondUE down to the lower layer(s) after a Link Identifier UpdateAcknowledgement (ACK) message is passed to the lower layer(s) fortransmission in response to reception of the Link Identifier UpdateAccept message.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram of a wireless communication system according toone exemplary embodiment.

FIG. 2 is a block diagram of a transmitter system (also known as accessnetwork) and a receiver system (also known as user equipment or UE)according to one exemplary embodiment.

FIG. 3 is a functional block diagram of a communication system accordingto one exemplary embodiment.

FIG. 4 is a functional block diagram of the program code of FIG. 3according to one exemplary embodiment.

FIG. 5 is a reproduction of FIG. 6.1.2.2.2 of 3GPP TS 24.587 V2.0.0.

FIG. 6 is a reproduction of FIG. 6.1.2.5.2.1 of 3GPP TS 24.587 V2.0.0.

FIG. 7 is a flow chart illustrating Layer-2 ID change over unicast linkbetween UE1 and UE2 according to one exemplary embodiment.

FIG. 8 is a flow chart illustrating another scenario (in addition to theexemplary scenario shown in FIG. 7 ) for both UEs taking privacy timerinto account according to one embodiment.

FIG. 9 is a flow chart according to one exemplary embodiment.

DETAILED DESCRIPTION

The exemplary wireless communication systems and devices described belowemploy a wireless communication system, supporting a broadcast service.Wireless communication systems are widely deployed to provide varioustypes of communication such as voice, data, and so on. These systems maybe based on code division multiple access (CDMA), time division multipleaccess (TDMA), orthogonal frequency division multiple access (OFDMA),3GPP LTE (Long Term Evolution) wireless access, 3GPP LTE-A orLTE-Advanced (Long Term Evolution Advanced), 3GPP2 UMB (Ultra MobileBroadband), WiMax, 3GPP NR (New Radio), or some other modulationtechniques.

In particular, the exemplary wireless communication systems devicesdescribed below may be designed to support one or more standards such asthe standard offered by a consortium named “3rd Generation PartnershipProject” referred to herein as 3GPP, including: TS24.587 v2.0.0,“Vehicle-to-Everything (V2X) services in 5G System (5GS) Stage 3”. Thestandards and documents listed above are hereby expressly incorporatedby reference in their entirety.

FIG. 1 shows a multiple access wireless communication system accordingto one embodiment of the invention. An access network 100 (AN) includesmultiple antenna groups, one including 104 and 106, another including108 and 110, and an additional including 112 and 114. In FIG. 1 , onlytwo antennas are shown for each antenna group, however, more or fewerantennas may be utilized for each antenna group. Access terminal 116(AT) is in communication with antennas 112 and 114, where antennas 112and 114 transmit information to access terminal 116 over forward link120 and receive information from access terminal 116 over reverse link118. Access terminal (AT) 122 is in communication with antennas 106 and108, where antennas 106 and 108 transmit information to access terminal(AT) 122 over forward link 126 and receive information from accessterminal (AT) 122 over reverse link 124. In a FDD system, communicationlinks 118, 120, 124 and 126 may use different frequency forcommunication. For example, forward link 120 may use a differentfrequency then that used by reverse link 118.

Each group of antennas and/or the area in which they are designed tocommunicate is often referred to as a sector of the access network. Inthe embodiment, antenna groups each are designed to communicate toaccess terminals in a sector of the areas covered by access network 100.

In communication over forward links 120 and 126, the transmittingantennas of access network 100 may utilize beamforming in order toimprove the signal-to-noise ratio of forward links for the differentaccess terminals 116 and 122. Also, an access network using beamformingto transmit to access terminals scattered randomly through its coveragecauses less interference to access terminals in neighboring cells thanan access network transmitting through a single antenna to all itsaccess terminals.

An access network (AN) may be a fixed station or base station used forcommunicating with the terminals and may also be referred to as anaccess point, a Node B, a base station, an enhanced base station, anevolved Node B (eNB), or some other terminology. An access terminal (AT)may also be called user equipment (UE), a wireless communication device,terminal, access terminal or some other terminology.

FIG. 2 is a simplified block diagram of an embodiment of a transmittersystem 210 (also known as the access network) and a receiver system 250(also known as access terminal (AT) or user equipment (UE)) in a MIMOsystem 200. At the transmitter system 210, traffic data for a number ofdata streams is provided from a data source 212 to a transmit (TX) dataprocessor 214.

In one embodiment, each data stream is transmitted over a respectivetransmit antenna. TX data processor 214 formats, codes, and interleavesthe traffic data for each data stream based on a particular codingscheme selected for that data stream to provide coded data.

The coded data for each data stream may be multiplexed with pilot datausing OFDM techniques. The pilot data is typically a known data patternthat is processed in a known manner and may be used at the receiversystem to estimate the channel response. The multiplexed pilot and codeddata for each data stream is then modulated (i.e., symbol mapped) basedon a particular modulation scheme (e.g., BPSK, QPSK, M-PSK, or M-QAM)selected for that data stream to provide modulation symbols. The datarate, coding, and modulation for each data stream may be determined byinstructions performed by processor 230.

The modulation symbols for all data streams are then provided to a TXMIMO processor 220, which may further process the modulation symbols(e.g., for OFDM). TX MIMO processor 220 then provides N_(T) modulationsymbol streams to N_(T) transmitters (TMTR) 222 a through 222 t. Incertain embodiments, TX MIMO processor 220 applies beamforming weightsto the symbols of the data streams and to the antenna from which thesymbol is being transmitted.

Each transmitter 222 receives and processes a respective symbol streamto provide one or more analog signals, and further conditions (e.g.,amplifies, filters, and upconverts) the analog signals to provide amodulated signal suitable for transmission over the MIMO channel. N_(T)modulated signals from transmitters 222 a through 222 t are thentransmitted from N_(T) antennas 224 a through 224 t, respectively.

At receiver system 250, the transmitted modulated signals are receivedby N_(R) antennas 252 a through 252 r and the received signal from eachantenna 252 is provided to a respective receiver (RCVR) 254 a through254 r. Each receiver 254 conditions (e.g., filters, amplifies, anddownconverts) a respective received signal, digitizes the conditionedsignal to provide samples, and further processes the samples to providea corresponding “received” symbol stream.

An RX data processor 260 then receives and processes the N_(R) receivedsymbol streams from N_(R) receivers 254 based on a particular receiverprocessing technique to provide N_(T) “detected” symbol streams. The RXdata processor 260 then demodulates, deinterleaves, and decodes eachdetected symbol stream to recover the traffic data for the data stream.The processing by RX data processor 260 is complementary to thatperformed by TX MIMO processor 220 and TX data processor 214 attransmitter system 210.

A processor 270 periodically determines which pre-coding matrix to use(discussed below). Processor 270 formulates a reverse link messagecomprising a matrix index portion and a rank value portion.

The reverse link message may comprise various types of informationregarding the communication link and/or the received data stream. Thereverse link message is then processed by a TX data processor 238, whichalso receives traffic data for a number of data streams from a datasource 236, modulated by a modulator 280, conditioned by transmitters254 a through 254 r, and transmitted back to transmitter system 210.

At transmitter system 210, the modulated signals from receiver system250 are received by antennas 224, conditioned by receivers 222,demodulated by a demodulator 240, and processed by a RX data processor242 to extract the reserve link message transmitted by the receiversystem 250. Processor 230 then determines which pre-coding matrix to usefor determining the beamforming weights then processes the extractedmessage.

Turning to FIG. 3 , this figure shows an alternative simplifiedfunctional block diagram of a communication device according to oneembodiment of the invention. As shown in FIG. 3 , the communicationdevice 300 in a wireless communication system can be utilized forrealizing the UEs (or ATs) 116 and 122 in FIG. 1 or the base station (orAN) 100 in FIG. 1 , and the wireless communications system is preferablythe LTE or NR system. The communication device 300 may include an inputdevice 302, an output device 304, a control circuit 306, a centralprocessing unit (CPU) 308, a memory 310, a program code 312, and atransceiver 314. The control circuit 306 executes the program code 312in the memory 310 through the CPU 308, thereby controlling an operationof the communications device 300. The communications device 300 canreceive signals input by a user through the input device 302, such as akeyboard or keypad, and can output images and sounds through the outputdevice 304, such as a monitor or speakers. The transceiver 314 is usedto receive and transmit wireless signals, delivering received signals tothe control circuit 306, and outputting signals generated by the controlcircuit 306 wirelessly. The communication device 300 in a wirelesscommunication system can also be utilized for realizing the AN 100 inFIG. 1 .

FIG. 4 is a simplified block diagram of the program code 312 shown inFIG. 3 in accordance with one embodiment of the invention. In thisembodiment, the program code 312 includes an application layer 400, aLayer 3 portion 402, and a Layer 2 portion 404, and is coupled to aLayer 1 portion 406. The Layer 3 portion 402 generally performs radioresource control. The Layer 2 portion 404 generally performs linkcontrol. The Layer 1 portion 406 generally performs physicalconnections.

3GPP TS 24.587 introduced the following procedures forVehicle-to-Everything (V2X) communication over PC5 interface as follows:

6.1 V2X Communication Over PC5 6.1.1 General

This clause describes the procedures at the UE, and between UEs, for V2Xcommunication over PC5.

The UE shall support requirements for securing V2X communication overPC5.

Both IP based and non-IP based V2X communication over PC5 are supported.For IP based V2X communication, only IPv6 is used. IPv4 is not supportedin this release of the present document.

V2X messages carried over PC5 are exchanged using user plane and theycan be sent or received over broadcast, unicast or groupcast dependingon whether the user equipment (UE) is using the new radio (NR-PC5) orthe evolved universal terrestrial radio access (E-UTRA-PC5).

NOTE: Further details about whether broadcast, unicast or groupcast canbe used over PC5 are described in 3GPP TS 23.287 [3] clause 5.2.1.

6.1.2 Unicast Mode Communication Over NR Based PC5 6.1.2.1 Overview

This clause describes the PC5 signalling protocol procedures between twoUEs for unicast mode of V2X communication. The following PC5 signallingprotocol procedures are defined:

-   a) PC5 unicast link establishment;-   b) PC5 unicast link modification;-   c) PC5 unicast link release;-   d) PC5 unicast link identifier update;-   e) PC5 unicast link authentication;-   f) PC5 unicast link security mode control; and-   g) PC5 unicast link keep-alive.

6.1.2.2 PC5 Unicast Link Establishment Procedure 6.1.2.2.1 General

The PC5 unicast link establishment procedure is used to establish a PC5unicast link between two UEs. The UE sending the request message iscalled the “initiating UE” and the other UE is called the “target UE”.

6.1.2.2.2 PC5 Unicast Link Establishment Procedure Initiation byinitiating UE

The initiating UE shall meet the following pre-conditions beforeinitiating this procedure:

-   a) a request from upper layers to transmit the packet for V2X    service over PC5;-   b) the link layer identifier for the initiating UE (i.e. layer 2 ID    used for unicast communication) is available (e.g. pre-configured or    self-assigned);-   c) the link layer identifier for the unicast initial signaling (i.e.    destination layer 2 ID used for unicast initial signaling) is    available to the initiating UE (e.g. pre-configured, obtained as    specified in clause 5.2.3 or known via prior V2X communication);-   d) the initiating UE is either authorised for V2X communication over    PC5 in NR in the serving PLMN, or has a valid authorization for V2X    communication over PC5 in NR when not served by E-UTRAN and not    served by NR; and-   e) there is no existing PC5 unicast link for the pair of peer    application layer IDs and the network layer protocol of this PC5    unicast link are identical to those required by the upper layer in    the initiating UE for this V2X service.

In order to initiate the PC5 unicast link establishment procedure, theinitiating UE shall create a DIRECT LINK ESTABLISHMENT REQUEST message.The initiating UE:

-   a) shall include the source user info set to the initiating UE’s    application layer ID received from upper layers;-   b) shall include the V2X service identifier received from upper    layer;-   c) may include the target user info set to the target UE’s    application layer ID if received from upper layers; and-   d) shall include the security establishment information.

After the DIRECT LINK ESTABLISHMENT REQUEST message is generated, theinitiating UE shall pass this message to the lower layers fortransmission along with the initiating UE’s Layer 2 ID for unicastcommunication and the destination layer 2 ID used for unicast initialsignaling, and start timer T5000. The UE shall not send a new DIRECTLINK ESTABLISHMENT REQUEST message to the same target UE identified bythe same application layer ID while timer T5000 is running.

[FIG. 6.1.2.2.2 of 3GPP TS 24.587 V2.0.0, entitled “PC5 unicast linkestablishment procedure”, is reproduced as FIG. 5] 6.1.2.2.3 PC5 UnicastLink Establishment Procedure Accepted by the Target UE

Upon receipt of a DIRECT LINK ESTABLISHMENT REQUEST message, the targetUE shall assign a layer-2 ID for this PC5 unicast link and store thisassigned layer-2 ID and the source layer 2 ID used in the transport ofthis message provided by the lower layers. This pair of layer-2 IDs isassociated with a PC5 unicast link context.

If:

-   a) the target user info IE is included in the DIRECT LINK    ESTABLISHMENT REQUEST message and this IE includes the target UE’s    application layer ID; or-   b) the target user info IE is not included in the DIRECT LINK    ESTABLISHMENT REQUEST message and the target UE is interested in the    V2X service identified by the V2X service identifier in the DIRECT    LINK ESTABLISHMENT REQUEST message;

then the target UE shall either identify an existing security contextwith the initiating UE, or establish a new security context byperforming one or more PC5 unicast link authentication procedures asspecified in clause 6.1.2.6, and performing the PC5 unicast linksecurity mode control procedure as specified in clause 6.1.2.7.

Upon successful completion of the PC5 unicast link security mode controlprocedure, in order to determine whether the DIRECT LINK ESTABLISHMENTREQUEST message can be accepted or not, in case of IP communication, thetarget UE checks whether there is at least one common IP addressconfiguration option supported by both the initiating UE and the targetUE.

If the target UE accepts the PC5 unicast link establishment procedure,the target UE shall create a DIRECT LINK ESTABLISHMENT ACCEPT message.The target UE:

-   a) shall include the source user info set to the target UE’s    application layer ID received from upper layers;-   b) shall include a PQFI and the corresponding PC5 QoS parameters;-   c) may include an IP address configuration IE set to one of the    following values if IP communication is used:    -   1) “IPv6 router” if only IPv6 address allocation mechanism is        supported by the target UE, i.e. acting as an IPv6 router; or    -   2) “IPv6 address allocation not supported” if IPv6 address        allocation mechanism is not supported by the target UE;-   d) may include a link local IPv6 address IE formed locally based on    IETF RFC 4862 [16] if IP address configuration IE is set to “IPv6    address allocation not supported” and the received DIRECT LINK    ESTABLISHMENT REQUEST message included a link local IPv6 address IE.

6.1.2.2.4 PC5 Unicast Link Establishment Procedure Completion by TheInitiating UE

Upon receipt of the DIRECT LINK ESTABLISHMENT ACCEPT message, theinitiating UE shall stop timer T5000 and store the source layer-2 ID andthe destination Layer-2 ID used in the transport of this messageprovided by the lower layers. This pair of layer-2 IDs shall beassociated with a PC5 unicast link context. From this time onward theinitiating UE shall use the established link for V2X communication overPC5 and additional PC5 signalling messages to the target UE.

6.1.2.5 PC5 Unicast Link Identifier Update Procedure 6.1.2.5.1 General

The PC5 unicast link identifier update procedure is used to update andexchange the new identifiers (e.g. application layer ID, layer 2 ID,security information and IP address/prefix) between two UEs for a PC5unicast link before using the new identifiers. The UE sending the DIRECTLINK IDENTIFIER UPDATE REQUEST message is called the “initiating UE” andthe other UE is called the “target UE”.

6.1.2.5.2 PC5 Unicast Link Identifier Update Procedure Initiation ByInitiating UE

The initiating UE shall initiate the procedure if:

-   a) the initiating UE receives a request from upper layers to change    the Application Layer ID and there is an existing PC5 unicast link    associated with this Application Layer ID; or-   b) the privacy timer of the initiating UE’s layer 2 ID expires for    an existing PC5 unicast link.

If the PC5 unicast link identifier update procedure is triggered by achange of the initiating UE’s application layer ID, the initiating UEshall create a DIRECT LINK IDENTIFIER UPDATE REQUEST message. In thismessage, the initiating UE

-   a) shall include the initiating UE’s new application layer ID    received from upper layer;-   b) shall include the initiating UE’s new layer 2 ID assigned by    itself;-   c) shall include the new security information; and-   d) may include the new IP address/prefix if IP communication is    used.

If the PC5 unicast link identifier update procedure is triggered by theexpiry of the initiating UE’s privacy timer as specified in clause5.2.3, the initiating UE shall create a DIRECT LINK IDENTIFIER UPDATEREQUEST message. In this message, the initiating UE

-   a) shall include the initiating UE’s new layer 2 ID assigned by    itself;-   b) shall include the new security information;-   c) may include the initiating UE’s new application layer ID received    from upper layer; and-   d) may include the new IP address/prefix if IP communication is    used.

After the DIRECT LINK IDENTIFIER UPDATE REQUEST message is generated,the initiating UE shall pass this message to the lower layers fortransmission along with the initiating UE’s old Layer 2 ID and thetarget UE’s Layer 2 ID, and start timer T5003. The UE shall not send anew DIRECT LINK IDENTIFIER UPDATE REQUEST message to the same target UEwhile timer T5003 is running.

[FIG. 6.1.2.5.2.1 of 3GPP TS 24.587 V2.0.0, Entitled “PC5 Unicast LinkIdentifier Update Procedure”, is Reproduced as FIG. 6] 6.1.2.5.3 PC5Unicast Link Identifier Update Procedure Accepted by the Target UE

Upon receipt of a DIRECT LINK IDENTIFIER UPDATE REQUEST message, if thetarget UE determines:

-   a) the PC5 unicast link associated with this request message is    still valid; and-   b) the timer T5004 for the PC5 unicast link identified by this    request message is not running, then the target UE accepts this    request and responds with a DIRECT LINK IDENTIFIER UPDATE ACCEPT    message.

If the target UE has the privacy configuration as specified in clause5.2.3 and decides to change its identifier, the target UE shall createthe DIRECT LINK IDENTIFIER UPDATE ACCEPT message. In this message, thetarget UE:

-   a) shall include the target UE’s new layer 2 ID assigned by itself;-   b) shall include the new security information;-   c) may include the target UE’s new application layer ID received    from upper layer; and-   d) may include the new IP address/prefix if IP communication is    used.

After the DIRECT LINK IDENTIFIER UPDATE ACCEPT message is generated, thetarget UE shall pass this message to the lower layers for transmissionalong with the initiating UE’s old Layer 2 ID and the target UE’s oldLayer 2 ID, and start timer T5004. The UE shall not send a new DIRECTLINK IDENTIFIER UPDATE ACCEPT message to the same initiating UE whiletimer T5004 is running.

Before target UE receives the traffic using the new layer-2 IDs, thetarget UE shall continue to receive the traffic with the old layer-2 IDs(i.e. initiating UE’s old layer-2 ID and target UE’s old layer-2 ID)from initiating UE.

Before target UE receives the DIRECT LINK IDENTIFIER UPDATE ACK messagefrom initiating UE, the target UE shall keep sending traffic to theinitiating UE using the old layer-2 IDs (i.e. initiating UE’s oldlayer-2 ID and target UE’s old layer-2 ID).

6.1.2.5.4 PC5 Unicast Link Identifier Update Procedure Acknowledged bythe Initiating UE

Upon receipt of the DIRECT LINK IDENTIFIER UPDATE ACCEPT message, theinitiating UE shall stop timer T5003 and respond with a DIRECT LINKIDENTIFIER UPDATE ACK message. In this message, the initiating UE:

-   a) shall include the target UE’s new layer 2 ID, if received;-   b) shall include the target UE’s new security information, if    received;-   c) may include the target UE’s new application layer ID, if    received; and-   d) may include the new IP address/prefix, if received.

Upon receipt of the DIRECT LINK IDENTIFIER UPDATE ACCEPT message. theinitiating UE shall update the associated PC5 unicast link context withthe new identifiers, and pass the initiating UE’s new Layer 2 ID and thetarget UE’s new Layer 2 ID down to the lower layer.

After the DIRECT LINK IDENTIFIER UPDATE ACK message is generated, theinitiating UE shall pass this message to the lower layers fortransmission along with the initiating UE’s old Layer 2 ID and thetarget UE’s old Layer 2 ID.

The initiating UE shall continue to receive traffic with the old layer-2IDs (i.e. initiating UE’s old layer-2 ID and target UE’s old layer-2 ID)from the target UE until it receives traffic with the new layer-2 IDs(i.e. initiating UE’s new layer-2 ID and target UE’s new layer-2 ID)from the target UE.

6.1.2.5.5 PC5 Unicast Link Identifier Update Procedure Completion by theTarget UE

Upon receipt of the DIRECT LINK IDENTIFIER UPDATE ACK message, thetarget UE shall update the associated PC5 unicast link context with thenew identifiers, pass the new initiating UE’s Layer 2 ID and the newtarget UE’s Layer 2 ID down to the lower layer and stop timer T5004.

In 3GPP TS 24.587, a procedure used to update L2ID (i.e. PC5 unicastlink identifier update procedure) was introduced. This procedure is usedto update the peer UE in the unicast communication of the impendingchange of the identifiers used for this unicast link. Due to the privacyrequirements, in eV2X use, UE should frequently change its identifiersin order to avoiding being trackable by 3rd party. When the identifierchange happens, all identifiers across all the layers, i.e. fromapplication layer ID to L2 ID, need to be changed. This signalling isrequired before the identifier changes happen, to prevent serviceinterruptions.

Possibly, the PC5 unicast link identifier update procedure could beinitialized by an initiating UE when the initiating UE receives arequest from upper layers to change the Application Layer ID or theprivacy timer of the initiating UE’s Layer-2 ID expires. In a unicastlink, since Layer-2 ID used for transmission and reception on theunicast link is assigned by UE itself, both UEs of the unicast linkmaintain its privacy timer of its Layer-2 ID.

FIG. 7 is an exemplary flow chart illustrating Layer-2 ID change overunicast link between UE1 and UE2 according to one embodiment. In thebeginning, UE1 would like to establish a unicast link with UE2. Thus,UE1 transmits a Link Establishment Request message (e.g. DIRECT LINKESTABLISHMENT REQUEST in 3GPP TS 24.587) to UE2. For this unicast link,UE1 assigns a Layer-2 ID (L2ID) “ID1-1” by itself, and uses this L2ID totransmit the Link Establishment Request message.

Upon reception of the Link Establishment Request message, UE2 decides toestablish the unicast link with UE1. Therefore, UE2 responds a LinkEstablishment Accept message (e.g. DIRECT LINK ESTABLISHMENT ACCEPT in3GPP TS 24.587) to UE1. Similarly, UE2 assigns a L2ID “ID2-1” for thisunicast link and uses this L2ID to transmit the Link EstablishmentAccept message.

Upon expiry of the privacy timer of UE1 for this unicast link, UE1decides to change its old L2ID “ID1-1” to a new L2ID “ID1-2”. For thischange, UE1 initializes the PC5 unicast link identifier updateprocedure. UE1 transmits a Link ID Update Request message (e.g. DIRECTLINK IDENTIFIER UPDATE REQUEST) to UE2. In the Link ID Update Requestmessage, the new L2ID “ID1-2” of UE1 is included.

Upon reception of the Link ID Update Request message, UE2 also changesits old L2ID “ID2-1” to a new L2ID “ID2-2” and then responds a Link IDUpdate Accept message (e.g. DIRECT LINK IDENTIFIER UPDATE ACCEPT) toUE1. In the Link ID Update Accept message, the new L2ID “ID2-2” of UE2is included.

Upon reception of the Link ID Update Accept message, UE1 responds a LinkID Update ACK message (e.g. DIRECT LINK IDENTIFIER UPDATE ACK) to UE2.According to 3GPP TS 24.587, UE1 will update the L2IDs of the unicastlink to the new L2ID “ID1-2” of UE1 and the new L2ID “ID2-2” of UE2 andpass the updated L2IDs to lower layers for sidelinktransmission/reception on the unicast link. In the Link ID Update ACKmessage, the L2ID “ID2-2” of UE2 is included.

Upon reception of the Link ID Update ACK message, UE2 will update theL2IDs of the unicast link to the new L2ID “ID1-2” of UE1 and the newL2ID “ID2-2” of UE2, and will pass the updated L2IDs to lower layers forsidelink transmission/reception on the unicast link.

FIG. 8 is an exemplary flow chart illustrating another scenario (inaddition to the exemplary scenario shown in FIG. 7 ) for both UEs takingprivacy timer into account according to one embodiment. UE1 initializesa first PC5 link identifier update procedure with UE2 when the privacytimer of UE1 expires. Thus, UE1 transmits a Link ID Update Request #1message to UE2. In the Link ID Update Request #1 message, a new L2ID “ID1-2” of UE1 is included. Possibly, at this moment, the privacy timer ofUE2 also expires so that UE2 initializes a second PC5 link identifierupdate procedure with UE1. Thus, UE2 transmits a Link ID Update Request#2 message to UE1. In the Link ID Update Request #2 message, a new L2ID“ID2-2” of UE2 is included. Since UE2 has not received the Link IDUpdate Request #1 message from UE1 yet, UE2 does not know UE1 hasperformed the first PC5 link identifier update procedure.

If the concept of PC5 link identifier update procedure introduced in3GPP TS 24.587 and illustrated in FIG. 7 is followed, a new Layer-2 IDshould be assigned when a Link ID Update Request message is received anda Link ID Update Accept message should be sent in response to receptionof the Link ID Update Request message. Therefore, UE2 will change againa new L2ID “ID2-3” for the unicast link when the Link ID Update Request#1 message is received and transmit a Link ID Update Accept #1 messageincluding the new L2ID “ID2-3” to UE1 in response to reception of theLink ID Update Request #1 message. Similarly, UE1 will change again anew L2ID “ID 1-3” for the unicast link when the Link ID Update Request#2 message is received, and will transmit a Link ID Update Accept #2message including the new L2ID “ID 1-3” to UE2 in response to receptionof the Link ID Update Request #2 message.

In response to reception of the Link ID Update Accept #1 message, UE1transmits a Link ID Update ACK #1 message to UE2. Since a Link ID UpdateACK message includes a target UE’s new Layer-2 ID included in acorresponding Link ID Update Accept message sent by the target UE, UE1includes the L2ID “ID2-3” included in the Link ID Update Accept #1message in the Link ID Update ACK #1 message. Similarly, in response toreception of the Link ID Update Accept #2 message, UE2 transmits a LinkID Update ACK #2 message to UE1. UE2 includes the L2ID “ID1-3” includedin the Link ID Update Accept #2 message in the Link ID Update ACK #2message.

Upon reception of the Link ID Update ACK #1 message, UE2 updates L2IDsof the unicast link to the L2ID “ID1-2” of UE1 (as included in the LinkID Update Request #1 message) and the L2ID “ID2-3” of UE2 (as includedin the Link ID Update Accept #1 message). On the other hand, uponreception of the Link ID Update ACK #2 message, UE1 updates L2IDs of theunicast link to the L2ID “ID 1-3” of UE1 (as included in the Link IDUpdate Accept #2 message) and the L2ID “ID2-2” of UE2 (as included inthe Link ID Update Request #2 message). As a result, both UEs usedifferent L2ID pair for communicating each other on the unicast link andretransmissions using wrong L2ID pair will reach maximum retransmissionopportunities in lower layers (e.g. at RLC layer, MAC layer or PHYlayer) that will cause radio link failure.

According to 3GPP TS 24.587, the initiating UE should start timer T5003when a Link ID Update Request message is generated for transmission, andshould stop timer T5003 when a Link ID Update Accept messagecorresponding to the Link ID Update Request message is received from thetarget UE.

To address the L2ID pair misalignment issue, UE2 could include the L2ID“ID2-2”, which has been included in the Link ID Update Request #2message, in the Link ID Update Accept #1 message if such timer T5003 ofUE2 for the Link ID Update Request #2 message is running. In otherwords, UE2 cannot assign a second new Layer-2 ID (e.g. “ID2-3”) when theLink ID Update Request #1 message is received from UE1 but such timerT5003 of UE2 for the Link ID Update Request #2 message is still running.

From UE1′s point of view, UE1 could include the L2ID “ID 1-2”, which hasbeen included in the Link ID Update Request #1 message, in the Link IDUpdate Accept #2 message if such timer T5003 of UE1 for the Link IDUpdate Request #1 message is running, which means UE1 cannot assign asecond new Layer-2 ID (e.g. “ID1-3”) when the Link ID Update Request #2message is received from UE2 but such timer T5003 of UE1 for the Link IDUpdate Request #1 message is still running.

With above solution, upon reception of the Link ID Update ACK #1message, UE2 could update L2IDs of the unicast link to the L2ID “ID 1-2” of UE1 (as included in the Link ID Update Request #1 message) and theL2ID “ID2-2” of UE2 (as included in the Link ID Update Accept #1 messageand the Link ID Update Request #2 message). On the other hand, uponreception of the Link ID Update ACK #2 message, UE1 could update L2IDsof the unicast link to the L2ID “ID 1-2” of UE1 (as included in the LinkID Update Accept #2 message and the Link ID Update Request #1 message)and the L2ID “ID2-2” of UE2 (as included in the Link ID Update Request#2 message). By this way, even if one PC5 unicast link identifier updateprocedure is performed on one side while another PC5 unicast linkidentifier update procedure is still ongoing on the other side, both UEscould still have the same L2ID pair for the unicast link after the bothprocedures are completed.

Alternatively, when one PC5 unicast link identifier update procedure isinitialized on one side while another PC5 unicast link identifier updateprocedure is already ongoing on the other side, one of them couldterminate or abort the ongoing PC5 unicast link identifier updateprocedure. Which UE terminates or aborts the ongoing PC5 unicast linkidentifier update procedure could be based on which UE requestsestablishment of the unicast link (e.g. this UE sends DIRECT LINKESTABLISHMENT REQUEST message). For example, when UE2 receives the LinkID Update Request #1 message from UE1 while the timer T5003 of UE2 isrunning, UE2 could stop the timer T5003 of UE2 (since UE2 is not the UErequesting establishment of the unicast link). UE2 still responds theLink ID Update Accept #1 message to UE1. In this case, UE2 could includethe L2ID “ID2-2” (as included in the Link ID Update Request #2 message)or the L2ID “ID2-3” (newly assigned due to reception of the Link IDUpdate Request #1 message) in the Link ID Update Accept #1 message. Onthe other hand, when UE1 receives the Link ID Update Request #2 messagefrom UE2 while the timer T5003 of UE1 is running, UE1 may not respondany message corresponding to the Link ID Update Request #2 message toUE2 (since UE1 is the UE requesting establishment of the unicast link).

Alternatively, UE1 may respond a Link ID Update Reject message (e.g.DIRECT LINK IDENTIFIER UPDATE REJECT) to UE2 when UE1 receives the LinkID Update Request #2 message from UE2 while the timer T5003 of UE1 isrunning. The Link ID Update Reject message may include a cause valuethat indicates UE1 had started a PC5 unicast link identifier updateprocedure. In this situation, UE2 could stop the timer T5003 of UE2 whenthe Link ID Update Reject message is received from UE1.

With the above alternatives, UE1 will not newly assign another new L2IDe.g. “ID1-3” due to reception of the Link ID Update Request #2 message.As usual, when UE1 receives the Link ID Update Accept #1 message, UE1could respond UE2 with the Link ID Update ACK #1 message including thenew L2ID of UE2 included in the Link ID Update Accept #1 message.

It may also be possible that which UE terminates or aborts the ongoingPC5 unicast link identifier update procedure could be based on which UEaccepts or completes establishment of the unicast link (e.g. this UEsends DIRECT LINK ESTABLISHMENT ACCEPT message). Therefore, the conceptof behaviours in above examples/alternatives can be also applied forthis possibility.

According to 3GPP TS 24.587, both the initiating UE and the target UEshould update their Layer-2 IDs during the PC5 unicast link identifierupdate procedure. In other words, since one side always updates itsLayer-2 ID when the other side updates its Layer-2 ID via the PC5unicast link identifier update procedure, there is no need to maintainsuch privacy timer on each side. Therefore, one alternative could bethat one of both UEs maintains the privacy timer of the unicast link.For example, either the initiating UE or the target UE could maintainthe privacy timer for updating the L2ID pair of the unicast link. If thescenario illustrated in FIG. 8 applies this alternative, the second PC5unicast link identifier update procedure would not be performed due toexpiry of the privacy timer while the first PC5 unicast link identifierupdate procedure is ongoing. Thus, the L2ID pair misalignment in thisscenario could also be addressed.

More specifically, the initiating UE could be the UE that requests aunicast link establishment (e.g. sending DIRECT LINK ESTABLISHMENTREQUEST). And, the target UE could be the UE that accepts or completesthe unicast link establishment (e.g. sending DIRECT LINK ESTABLISHMENTACCEPT).

According to Section 6.1.2.5.4 of 3GPP TS 24.587, upon receipt of theDIRECT LINK IDENTIFIER UPDATE ACCEPT message, the initiating UE shallupdate the associated PC5 unicast link context with the new identifiers,and pass the initiating UE’s new Layer 2 ID and the target UE’s newLayer 2 ID down to the lower layer. This implies that the lower layer(s)in the initiating UE may start data packet transmission using new L2 IDsafter receiving the DIRECT LINK IDENTIFIER UPDATE ACCEPT message.

In addition, Section 6.1.2.5.5 of 3GPP TS 24.587 specifies that uponreceipt of the DIRECT LINK IDENTIFIER UPDATE ACK message, the target UEshall update the associated PC5 unicast link context with the newidentifiers and pass the new initiating UE’s Layer 2 ID and the newtarget UE’s Layer 2 ID down to the lower layer. Thus, the lower layer(s)in the target UE may start data packet reception using new L2 IDs afterreceiving the DIRECT LINK IDENTIFIER UPDATE ACK message. It is possiblethat data packets transmitted from the initiating UE may arrive at thetarget UE before the DIRECT LINK IDENTIFIER UPDATE ACK message becausethere may be data packets stored for transmission in the lower layer(s)of the initiating UE when the DIRECT LINK IDENTIFIER UPDATE ACCEPTmessage is received by the initiating UE. In this situation, these datapackets may be discarded by the lower layer(s) in the target UE becausethe lower layer(s) has not received the new Layer 2 IDs.

To solve the above issue, one potential solution is generally for theinitiating UE to pass the initiating UE’s new Layer 2 ID and the targetUE’s new Layer 2 ID down to the lower layer(s) after the DIRECT LINKIDENTIFIER UPDATE ACK message is generated or passed to the lowerlayer(s) for transmission. Another alternative to align the timings inboth UEs for using new Layer 2 IDs could be that the target UE passesthe initiating UE’s new Layer 2 ID and the target UE’s new Layer 2 IDdown to the lower layer(s) after the DIRECT LINK IDENTIFIER UPDATEACCEPT message is generated or passed to the lower layer(s) fortransmission (and before the DIRECT LINK IDENTIFIER UPDATE ACK messageis received from the initiating UE). In another alternative, the targetUE could pass the initiating UE’s new Layer 2 ID and the target UE’s newLayer 2 ID down to the lower layer(s) when the DIRECT LINK IDENTIFIERUPDATE ACCEPT message is generated or passed to the lower layer(s) fortransmission.

FIG. 9 is a flow chart 905 according to one exemplary embodiment fromthe perspective of a first UE for updating Layer-2 IDs. In step 905, thefirst UE establishes a unicast link with a second UE, wherein a firstLayer-2 ID of the first UE and a second Layer-2 ID of the second UE areused for data transmission and reception on the unicast link. In step910, the first UE transmits a Link Identifier Update Request message forthe unicast link to the second UE, wherein the Link Identifier UpdateRequest message includes a new first Layer-2 ID of the first UE. In step915, the first UE receives a Link Identifier Update Accept message forthe unicast link from the second UE, wherein the Link Identifier UpdateAccept message includes a new second Layer-2 ID of the second UE. Instep 920, the first UE passes the new first Layer-2 ID of the first UEand the new second Layer-2 ID of the second UE down to the lowerlayer(s) after a Link Identifier Update ACK message is passed to thelower layer(s) for transmission in response to reception of the LinkIdentifier Update Accept message.

In one embodiment, the first UE could transmit the Link IdentifierUpdate ACK message for the unicast link to the second UE with the firstLayer-2 ID of the first UE and the second Layer-2 ID of the second UE,wherein the Link Identifier Update ACK message includes the new secondLayer-2 ID of the second UE. The Link Identifier Update Request messagecould be a DIRECT LINK IDENTIFIER UPDATE REQUEST message, the LinkIdentifier Update Accept message could be a DIRECT LINK IDENTIFIERUPDATE ACCEPT message, and the Link Identifier Update ACK message couldbe a DIRECT LINK IDENTIFIER UPDATE ACK message. The lower layer(s) couldbe a Radio Link Control (RLC) layer, a Medium Access Control (MAC)layer, and/or a Physical (PHY) layer of the first UE.

Referring back to FIGS. 3 and 4 , in one exemplary embodiment of a firstUE. The first UE 300 includes a program code 312 stored in the memory310. The CPU 308 could execute program code 312 to enable the first UE(i) to establish a unicast link with a second UE, wherein a firstLayer-2 ID of the first UE and a second Layer-2 ID of the second UE areused for data transmission and reception on the unicast link, (ii) totransmit a Link Identifier Update Request message for the unicast linkto the second UE, wherein the Link Identifier Update Request messageincludes a new first Layer-2 ID of the first UE, (iii) to receive a LinkIdentifier Update Accept message for the unicast link from the secondUE, wherein the Link Identifier Update Accept message includes a newsecond Layer-2 ID of the second UE, and (iv) to pass the new firstLayer-2 ID of the first UE and the new second Layer-2 ID of the secondUE down to the lower layer(s) after a Link Identifier Update ACK messageis passed to the lower layer(s) for transmission in response toreception of the Link Identifier Update Accept message. Furthermore, theCPU 308 can execute the program code 312 to perform all of theabove-described actions and steps or others described herein.

Various aspects of the disclosure have been described above. It shouldbe apparent that the teachings herein could be embodied in a widevariety of forms and that any specific structure, function, or bothbeing disclosed herein is merely representative. Based on the teachingsherein one skilled in the art should appreciate that an aspect disclosedherein could be implemented independently of any other aspects and thattwo or more of these aspects could be combined in various ways. Forexample, an apparatus could be implemented or a method could bepracticed using any number of the aspects set forth herein. In addition,such an apparatus could be implemented or such a method could bepracticed using other structure, functionality, or structure andfunctionality in addition to or other than one or more of the aspectsset forth herein. As an example of some of the above concepts, in someaspects concurrent channels could be established based on pulserepetition frequencies. In some aspects concurrent channels could beestablished based on pulse position or offsets. In some aspectsconcurrent channels could be established based on time hoppingsequences. In some aspects concurrent channels could be establishedbased on pulse repetition frequencies, pulse positions or offsets, andtime hopping sequences.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, processors, means, circuits, and algorithmsteps described in connection with the aspects disclosed herein may beimplemented as electronic hardware (e.g., a digital implementation, ananalog implementation, or a combination of the two, which may bedesigned using source coding or some other technique), various forms ofprogram or design code incorporating instructions (which may be referredto herein, for convenience, as “software” or a “software module”), orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentdisclosure.

In addition, the various illustrative logical blocks, modules, andcircuits described in connection with the aspects disclosed herein maybe implemented within or performed by an integrated circuit (“IC”), anaccess terminal, or an access point. The IC may comprise a generalpurpose processor, a digital signal processor (DSP), an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) or other programmable logic device, discrete gate or transistorlogic, discrete hardware components, electrical components, opticalcomponents, mechanical components, or any combination thereof designedto perform the functions described herein, and may execute codes orinstructions that reside within the IC, outside of the IC, or both. Ageneral purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

It is understood that any specific order or hierarchy of steps in anydisclosed process is an example of a sample approach. Based upon designpreferences, it is understood that the specific order or hierarchy ofsteps in the processes may be rearranged while remaining within thescope of the present disclosure. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

The steps of a method or algorithm described in connection with theaspects disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module (e.g., including executable instructions and relateddata) and other data may reside in a data memory such as RAM memory,flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a harddisk, a removable disk, a CD-ROM, or any other form of computer-readablestorage medium known in the art. A sample storage medium may be coupledto a machine such as, for example, a computer/processor (which may bereferred to herein, for convenience, as a “processor”) such theprocessor can read information (e.g., code) from and write informationto the storage medium. A sample storage medium may be integral to theprocessor. The processor and the storage medium may reside in an ASIC.The ASIC may reside in user equipment. In the alternative, the processorand the storage medium may reside as discrete components in userequipment. Moreover, in some aspects any suitable computer-programproduct may comprise a computer-readable medium comprising codesrelating to one or more of the aspects of the disclosure. In someaspects a computer program product may comprise packaging materials.

While the invention has been described in connection with variousaspects, it will be understood that the invention is capable of furthermodifications. This application is intended to cover any variations,uses or adaptation of the invention following, in general, theprinciples of the invention, and including such departures from thepresent disclosure as come within the known and customary practicewithin the art to which the invention pertains.

1. A method for a first User Equipment (UE) to update Layer-2 Identities(IDs), comprising: establishing a unicast link with a second UE, whereina first Layer-2 ID of the first UE and a second Layer-2 ID of the secondUE are used for at least one of data transmission or reception on theunicast link; generating a first Link Identifier Update Request message,comprising a new first Layer-2 ID of the first UE, of a procedure forupdating Layer-2 IDs for the unicast link; starting a timercorresponding to the procedure for updating Layer-2 IDs responsive togenerating the first Link Identifier Update Request message;transmitting the first Link Identifier Update Request message to thesecond UE; and stopping the timer if a second Link Identifier UpdateRequest message is received from the second UE when the timer isrunning.
 2. The method of claim 1, further comprising: transmitting aLink Identifier Update Accept message for the unicast link to the secondUE in response to reception of the second Link Identifier Update Requestmessage, wherein the Link Identifier Update Accept message comprises anew first Layer-2 ID of the first UE.
 3. The method of claim 2, furthercomprising: receiving a Link Identifier Update Acknowledgement (ACK)message for the unicast link from the second UE with the first Layer-2ID of the first UE and the second Layer-2 ID of the second UE, whereinthe Link Identifier Update ACK message comprises the new first Layer-2ID of the first UE.
 4. The method of claim 2, wherein the LinkIdentifier Update Accept message is a DIRECT LINK IDENTIFIER UPDATEACCEPT message.
 5. The method of claim 3, wherein the Link IdentifierUpdate ACK message is a DIRECT LINK IDENTIFIER UPDATE ACK message. 6.The method of claim 1, wherein the first Link Identifier Update Requestmessage is a DIRECT LINK IDENTIFIER UPDATE REQUEST message.
 7. Themethod of claim 1, further comprising: aborting the procedure forupdating Layer-2 IDs if the second Link Identifier Update Requestmessage is received from the second UE when the timer is running.
 8. Afirst User Equipment (UE), comprising: a control circuit; a processorinstalled in the control circuit; and a memory installed in the controlcircuit and operatively coupled to the processor; wherein the processoris configured to execute a program code stored in the memory to:establish a unicast link with a second UE, wherein a first Layer-2Identity (ID) of the first UE and a second Layer-2 ID of the second UEare used for at least one of data transmission or reception on theunicast link; generate a first Link Identifier Update Request message,comprising a new first Layer-2 ID of the first UE, of a procedure forupdating Layer-2 IDs for the unicast link; start a timer correspondingto the procedure for updating Layer-2 IDs responsive to generating thefirst Link Identifier Update Request message; transmit the first LinkIdentifier Update Request message to the second UE; and stop the timerif a second Link Identifier Update Request message is received from thesecond UE when the timer is running.
 9. The first UE of claim 8, furthercomprising: transmitting a Link Identifier Update Accept message for theunicast link to the second UE in response to reception of the secondLink Identifier Update Request message, wherein the Link IdentifierUpdate Accept message comprises a new first Layer-2 ID of the first UE.10. The first UE of claim 9, further comprising: receiving a LinkIdentifier Update Acknowledgement (ACK) message for the unicast linkfrom the second UE with the first Layer-2 ID of the first UE and thesecond Layer-2 ID of the second UE, wherein the Link Identifier UpdateACK message comprises the new first Layer-2 ID of the first UE.
 11. Thefirst UE of claim 9, wherein the Link Identifier Update Accept messageis a DIRECT LINK IDENTIFIER UPDATE ACCEPT message.
 12. The first UE ofclaim 10, wherein the Link Identifier Update ACK message is a DIRECTLINK IDENTIFIER UPDATE ACK message.
 13. The first UE of claim 8, whereinthe first Link Identifier Update Request message is a DIRECT LINKIDENTIFIER UPDATE REQUEST message.
 14. The first UE of claim 8, furthercomprising: aborting the procedure for updating Layer-2 IDs if thesecond Link Identifier Update Request message is received from thesecond UE when the timer is running.